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‎src/rimt-main.adoc‎

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== RISC-V IO Mapping Table (RIMT)
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The <<rimt>> shows the structure of RIMT. Apart from the basic header, RIMT can contain several
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nodes. Each node represents a component which can be an IOMMU, a PCIe root complex or a platform
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nodes. Each node represents a component, which can be an IOMMU, a PCIe root complex, or a platform
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device.
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.RISC-V IO Mapping Table
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|===
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==== IOMMU Node
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The IOMMU may be implemented as a platform device or as a PCIe device. The IOMMU node is
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The IOMMU can be implemented as a platform device or as a PCIe device. The IOMMU node is
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the structure in RIMT used to report the configuration and capabilities of each IOMMU in the system.
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.IOMMU Node
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| Revision | 1 | 1 | 1
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| Length | 2 | 2 | The length of this structure.
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| Reserved | 2 | 4 | Must be zero.
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| ID | 2 | 6 | Unique ID of this node in the RIMT which can
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| ID | 2 | 6 | Unique ID of this node in the RIMT that can
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be used to locate it in the RIMT node array.
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It can be simply the array index in the RIMT
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node array.
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| Hardware ID | 8 | 8 | ACPI ID of the IOMMU when it is a platform device
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or PCIe ID (Vendor ID + Device ID) for
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the PCIe IOMMU device.
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| Base Address | 8 | 16 | Base address of the IOMMU registers.
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This field is valid only for an IOMMU
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This field is valid for only an IOMMU
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that is a platform device. If IOMMU
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is a PCIe device, the base address of
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the IOMMU registers may be discovered
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domain.
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| PCIe Segment number | 2 | 32 | If the IOMMU is implemented as a PCIe
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device (Bit 0 of Flags is 1), then
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this field holds the PCIe segment on
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which this IOMMU is located.
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this field holds the PCIe segment
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where this IOMMU is located.
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| PCIe B/D/F | 2 | 34 | If the IOMMU is implemented as a PCIe
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device (Bit 0 of Flags is 1), then
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this field provides the
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Bus/Device/Function of the IOMMU.
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| Number of interrupt wires | 2 | 36 | An IOMMU may signal IOMMU initiated
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interrupts using wires or as message
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interrupts by using wires or as message
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signaled interrupts (MSI). When the
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IOMMU supports signaling interrupts
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using wires, this field provides the
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by using wires, this field provides the
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number of interrupt wires. This field
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must be 0 if the IOMMU does not
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support wire-based interrupt
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|===
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==== PCIe Root Complex Node
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The PCIe root complex node is the logical PCIe root complex which can be used to
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represent an entire physical root complex, an RCiEP/set of RCiEPs, a standalone PCIe device or the
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hierarchy below a PCIe host bridge.
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The PCIe root complex node is the logical PCIe root complex that can be used to
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represent an entire physical root complex, an RCiEP/set of RCiEPs, a standalone PCIe device, or the
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hierarchy following a PCIe host bridge.
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.PCIe Root Complex Node
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[[rc_node_structure]]
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|Revision | 1 | 1 | 1
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|Length | 2 | 2 | The length of this structure.
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|Reserved | 2 | 4 | Must be zero.
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| ID | 2 | 6 | Unique ID of this node in the RIMT which can
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| ID | 2 | 6 | Unique ID of this node in the RIMT that can
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be used to locate it in the RIMT node array.
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It can be simply the array index in the RIMT
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node array.
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See <<id_mapping_structure>>.
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|===
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The ID mapping structure provides information on how devices are connected to an IOMMU. The devices may be
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natively identified by a source ID but the platform may use a remapped ID to identify transactions from the
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The ID mapping structure provides information about how devices are connected to an IOMMU. The devices can be
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natively identified by a source ID, but the platform can use a remapped ID to identify transactions from the
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device to the IOMMU.
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For PCIe devices, source ID is the 16-bit triplet of PCIe bus number (8-bit), device number (5-bit), and
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function number (3-bit) (collectively known as routing identifier or RID). A range of source IDs must map to a
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single IOMMU only. If there are multiple root complexes with the same PCIe segment number, then their source
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ID ranges must not overlap. For each ACPI device object of the root complex which belongs to the same PCIe
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ID ranges must not overlap. For each ACPI device object of the root complex that belongs to the same PCIe
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segment, the firmware must include the Device Specific Method (_DSM), Function Index 5, for preserving boot
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configurations as defined by the PCI Firmware Specification cite:[PCI-FW-SPEC]. The _DSM method must return
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zero to indicate that the Operating System must preserve PCIe resource assignments made by the firmware at
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boot time.
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For platform devices, it is the implementation specific ID and managed by the device driver. Each ID mapping
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For platform devices, source ID is the implementation specific ID and managed by the device driver. Each ID mapping
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array entry provides a mapping from a range of source IDs to the corresponding device IDs that will be used at
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the input to the IOMMU. See <<Mapping-Examples>> for an example of ID mapping structures.
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as mapped by this entry. This is the
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*device_id* as defined by the RISC-V IOMMU
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specification cite:[IOMMU-SPEC]
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| Destination IOMMU Offset | 4 | 12 | The destination IOMMU with which the
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these IDs are associated. This field
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| Destination IOMMU Offset | 4 | 12 | The destination IOMMU that is associated
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with these IDs. This field
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is the offset of the RISC-V IOMMU
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node from the start of the RIMT
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table.
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|===
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==== Platform Device Node
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There may be non-PCIe platform devices which are enumerated using Differentiated System Description
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Table(DSDT). These devices may have one or more source IDs in the mapping table, but they can have
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their own scheme to define the source IDs. Hence, those source IDs can only be unique to the ACPI
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There may be non-PCIe platform devices that are enumerated by using Differentiated System Description
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Table(DSDT). These devices can have one or more source IDs in the mapping table, but they can have
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their own scheme to define the source IDs. Hence, those source IDs can be unique to only the ACPI
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platform device. The interpretation of those source IDs is expected to be managed by the platform
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device's device driver.
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| Revision | 1 | 1 | 1
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| Length | 2 | 2 | The length of this structure.
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| Reserved | 2 | 4 | Must be zero.
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| ID | 2 | 6 | Unique ID of this node in the RIMT which can
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| ID | 2 | 6 | Unique ID of this node in the RIMT that can
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be used to locate it in the RIMT node array.
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It can be simply the array index in the RIMT
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node array.

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